Security rules that apply to all accounts mean after every few contactless payments you will have to re-enter your PIN to use your card. Once you have done this your contactless payments should work again.
Please also make sure you make contactless payments under or up to the maximum limit allowed for contactless payments, this is usually £30 but has recently been increased since lockdown - to £100.
If your contactless payment is still not working, we advise you try different merchant and if this is still not working then you can contact us, and we will send you a new card free of charge.